1. Field of the Invention
The present invention relates to a wiper apparatus for wiping raindrops or the like from a glass, and particularly to a wiper apparatus for wiping a windshield glass of a vehicle.
2. Description of the Related Art
In a conventional wiper apparatus, in order to prevent the wiping performance from deteriorating when the vehicle travels at high speeds due to a wiper blade being lifted off of the windshield glass, a pressing force is applied to the wiper blade via a wiper arm so as to increase the force of pressing a blade rubber against the windshield glass, thereby increasing the press contact force between the blade rubber and the windshield glass surface. However, this causes a drawback in that the press contact force becomes greater than the force which is required when the vehicle is traveling at normal speeds, and thus greater noise is generated at the positions where the swinging direction of the wiper is reversed.
A wiper apparatus having a means for reducing noise generated when the swing of the wiper is reversed is disclosed, for example, in Japanese Utility Model Application Laid-open No. 2-117953. In the disclosed wiper apparatus, the pressing force applied to a wiper arm is reduced via a cam at the positions where the swing of the wiper is reversed. The structure of this wiping apparatus will be described with reference to FIG. 14A and FIG. 14B, wherein FIG. 14A shows a cross-section of the wiper along the longitudinal direction thereof and FIG. 14B is a schematic view showing a cam portion and a vicinity thereof.
As shown in FIG. 14A, an arm head 101 which swings over a windshield glass so as to wipe the windshield glass surface is fixed by a nut 104 to a pivot 103, which is fitted to a pivot holder 102 and extends through and projects from the arm head 101. More specifically, the nut 104 is screwed to an end of the pivot 103 so as to fix the arm head 101. A wiper arm 105 is pivotally mounted to the arm head 101 by using a coupling pin 106, and an unillustrated arm piece is attached to the wiper arm 105 so as to support a wiper blade (not shown).
One end of a coil spring 107 for varying a blade pressing force by its elasticity is anchored to an arm piece (not shown) supporting the wiper blade. The other end of the coil spring 107 is engaged with one end of a hook 108. The other end of the hook 108 is engaged with a coupling pin 109.
A lever 112 is supported by the arm head 101 via a coupling pin 113. A roller 111 is disposed at one end of the lever 112 so as to move on end cam surfaces 110a and on an intermediate cam surface 110b, which will be described later, of a cam portion 110. The other end of the lever 112 is engaged with the coupling pin 109.
The portion of the lever 112 between the coupling pin 113 and the roller 111 is bent substantially in an S shape so that the lever 112 is substantially parallel to the arm head 101 while the roller 111 moves on the end cam surfaces 110a.
As shown in FIG. 14B, the cam portion 110 is a structure in which the end cam surfaces 110a and the intermediate cam surface 110b are formed continuously. The roller 111 moves on the end cam surfaces 110a when the wiper blade is at its swing reversing positions. The intermediate cam surface 110b is positioned higher than the end cam surfaces 110a.
The action of the above-described wiper apparatus will now be described. While the roller 111 is moving on the end cam surface 110a, i.e., when the wiper is in a vicinity of one of its swing reversing positions, the lever 112 is in the state represented by the solid line, where the tensile direction of the coil spring 107 coincides with the center axis of the coil spring 107. Since one end of the coil spring 107 is engaged with the arm piece supporting the wiper blade, the elastic force of the coil spring 107 acts so as to pull on the arm piece, thereby reducing the pressing force applied to the wiper arm in a vicinity of the swing reversing position of the wiper. This reduces the noise generated when the swing of the wiper is reversed.
Subsequently, when the lever 112, together with the arm head 101, pivots about the pivot 103, the roller 111 abuts the cam surface of the cam portion 110 and then moves from the end cam surface 110a to the intermediate cam surface 110b. That is, after the wiper reverses its swing, the roller 111 is pushed up. This causes the lever 112 to push the coupling pin 109 down so that the lever 112 assumes the state represented by the two dots-and-dash line, since the lever 112 is supported by the coupling pin 113. As a result, the tensile direction of the coil spring 107 falls to below the axis of the coil spring 107, whereby a component force of the elastic force of the coil spring 107 acts as a tensile force which pulls on the arm piece. Consequently, the reduction in the pressing force is smaller than that in the vicinity of the swing reversing position of the wiper. That is, the wiper wipes the windshield glass without a significant reduction in the pressing force when the wiper is located at positions other than the swing reversing position.
However, in the wiper apparatus described above, since the cam which reduces the pressing force applied to the wiper arm at the swing reversing position of the wiper is distant from the blade rubber which is pressed against the windshield glass and which is a source of noise generated when the swing of the wiper is reversed, a change in the pressing force is transmitted to the blade rubber by varying the tensile force of the coil spring through coupling pins. That is, a varying force is transmitted via component parts from the cam, which is a point of force for varying the pressing force, to the contact position between the blade rubber and the windshield glass, which is a point of application.
Hence, a loss of force occurs at each of the component parts transmitting the varying force, resulting in an inability to efficiently transmit a change in force to the point of application. This presents a drawback in that noise generated when the swing of the wiper is reversed is not sufficiently reduced.